1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to arc hood assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to chimneys for circuit breaker arc hood assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include housing, and an operating mechanism which opens separable electrical contacts to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit.
Some low-voltage circuit breakers, for example, have arc chute vents on a portion (e.g., without limitation, the top) of the housing. When the separable electrical contacts rapidly open, for example, in response to an overload or short circuit condition, an arc is created which generates gases that are expelled from the vents. The gases can be extremely hot, are at least partly ionized, and may carry debris, such as molten metal particles. Furthermore, the gases and debris can be electrically conductive and, therefore, can cause additional undesirable arcing between the circuit breaker and grounded electrically conductive features proximate the circuit breaker, including but not limited to, the metallic enclosure in which such circuit breakers are typically installed. The gases may also be expelled with explosive force and may, therefore, damage components of the enclosure.
Accordingly, switchgear enclosures are typically designed to include one or more channels in which arc gases can be directed for dissipation thereof. Some switchgear cabinets also include an insulated barrier, commonly referred to as an arc hood, which is mounted above the arc chute vents of the circuit breaker through which the arc gases are exhausted. The arc hood functions to manage the effects of the arc gases and, in particular, to cool and dissipate the arc gases within the arc hood. However, there is room for improvement in arc hoods and, in particular, with respect to the interface (e.g., seal) between the arc hood, and the circuit breaker housing and the arc chute vents of the circuit breaker. Specifically, proper sealing is required in order to resist the escape of arc gases through gaps or openings between the circuit breaker and the arc hood, and to thereby avoid undesirable consequences associated therewith such as, for example, arcing across the poles of the circuit breaker and/or damage to components of the circuit breaker.
There is, therefore, room for improvement in arc hood assemblies for electrical switching apparatus, such as circuit breakers.